Eosin B/amine as photoinitiator system of vinyl polymerization. A photophysical study of the dye

Abstract

The photopolymerization of acrylamide in water under visible irradiation was initiated by the system eosin B/triethanolamine in deaerated conditions. In order to understand the mechanism of photoinitiation, the photophysics of the dye in the absence and presence of the amine was studied. The absorption and fluorescence properties in ethanol?water mixtures were determined. The fluorescence quantum yields were 0.003 and 0.02 in water and ethanol, respectively. The triplet state was observed by laser flash photolysis only in the alcohol. In water, the transient signal could not be detected. The triplet quantum yield was estimated at 0.08. In the absence of the amine or in air equilibrated solutions the polymer was not formed. Since no triplet is detected by laser flash photolysis in water, the question regarding the photoinitiation mechanism arises. It is suggested that, despite the lack of transient signal with our laser photolysis system, the triplet is formed in very low yield. Since the dye is photostable under the irradiation conditions of the polymerization experiments, in the long term polymerization could take place initiated by the triplet.